JPH06251781A - Manufacture of diaphragm for fuel cell having electrode catalyst layer on surface - Google Patents

Abstract

PURPOSE:To provide an easily manufactured and stable diaphragm for a fuel cell by introducing a sulfonic acid group in a fluorine polymer sheet after specific mixed solution is applied on the fluorine polymer sheet and it is dried and heat treatment is carried out. CONSTITUTION:Mixed solution of carbon particles carrying electrode catalyst particulates and fluorine contained sulfonic acid polymer is applied on a fluorine polymer sheet, and it is dried and heat treatment is carried out within a specific temperature range. A sulfonic acid group is introduced in this polymer sheet, and a diaphragm for a fuel cell is obtained. In this diaphragm, electrode catalyst layers 27 are applied on both sides of an ion exchange membrane 26, and the carbon particles 28 carrying the electrode catalyst particulates 29 are contained in the electrode catalyst layers 27, and these are contacted partially with each other, so that mutual electric conductivity can be secured. Proper pores 31 exist between the carbon particles, and play a role as a flow hole of gas to the electrode catalyst layers.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a fuel cell membrane having an electrode catalyst layer on the membrane constituting a fuel cell.

[0002]

2. Description of the Related Art In recent years, fuel cells have been attracting attention as a clean electric energy supply source. In particular, fuel cells using an ion-exchange membrane have a low operating energy of 100 ° C. or less. Due to its high density, it is expected to be used as a power source for transportation such as a power source for electric vehicles and a simple auxiliary power source. However, at present, a practical method for joining the electrode and the ion exchange membrane has not been established yet, and therefore the performance is not constant.

Among the elements required for the assembly of the fuel cell membrane and the electrode, particularly important are the low electrical resistance at the interface between the electrode and the membrane, and the electrical resistance of the membrane and the sulfonic acid polymer. It is low, does not have an excessive gas permeability, has excellent chemical durability and stability for long-term use, and has strong physical strength.

Fluorine-based ion exchange membranes currently used for fuel cells have polymer structures similar to those used in large quantities in ion exchange membrane chloralkali electrolysis, for example those manufactured by DuPont. An acid type such as Nafion (registered trademark) is often used. As the gas diffusion electrode, generally, carbon particles such as activated carbon on which fine platinum particles are supported and tetrafluoroethylene powder are mixed and hot-pressed, and have gas permeability and moderate hydrophobicity. Is used. Electrodes made by E-TEK are often used as this type of gas diffusion electrode.

However, when forming the bonded body of the fluorine-based ion exchange membrane and the gas diffusion electrode, the adhesion state at the bonded interface between the ion exchange membrane, which is the fuel cell diaphragm, and the gas diffusion electrode is unstable. However, inconveniences such as increased movement resistance of water and ions and increased electric resistance are likely to occur. Further, there is a problem that the utilization efficiency of the expensive electrode catalyst contained in the electrode is low.

Therefore, when the ion exchange membrane and the gas diffusion electrode are joined, a predetermined amount of a solution of an ion exchange resin component similar to the ion exchange membrane is applied in advance to the catalyst surface of the electrode, dried, and then integrated by hot pressing. Is joined to. The solution of the ion exchange resin component is, for example, about 5% in a mixed solution of water and an organic solvent such as propanol or ethyl alcohol, which is an acid type ion exchange resin such as Nafion (registered trademark) manufactured by DuPont. A dissolved product is often used.

However, when the solution containing the ion exchange resin component is applied to the gas diffusion electrode, the coating amount, the viscosity and the concentration of the solution containing the ion exchange resin component, the drying conditions for forming the film, etc. However, it was difficult to obtain reproducible results because the performance of the assembly of the electrode and the ion exchange membrane during fuel cell operation tended to vary. Further, the electrode itself is expensive, and it is not suitable for mass production because it requires a great deal of labor and effort to obtain a large-sized practical size electrode / ion exchange membrane assembly.

Other than that, Mahlon S. Wilson and Shmsho
n Gottesfeld (J. Electrochem. Soc., Vol.139, February 1
As shown in 992), a solution containing a powder in which platinum fine particles are supported on carbon particles, which is a constituent component of the gas diffusion electrode, and a solution in which the ion exchange resin component is replaced from an acid type to a salt type such as sodium is mixed. , It is coated on an ion-exchange membrane that has been replaced with a salt type such as sodium, and dried.
There is also a method of annealing at 190 ° C. to integrate them, and further substituting the ion exchange resin component from the salt form to the acid form.

However, even with this method, the solution containing the ion exchange resin component is difficult to dissolve if it is made into a salt form with, for example, sodium and is difficult to handle, and such an ion exchange resin component is added to a salt type ion exchange membrane such as sodium. When the solution containing the composition is applied and dried, there is a drawback that the film is easily peeled off or cracked, and it is difficult to obtain a homogeneous solution. Therefore, it was very difficult to mass-produce large-sized ones by this method.

In these methods, the utilization rate of the electrode catalyst and the bonding state with the ion exchange membrane are greatly improved. However, all of them are still laborious in the laboratory, and it is impossible to industrially obtain a bonded body of an ion exchange membrane and an electrode with a large size and a large amount of stable quality. It was close.

[0011]

SUMMARY OF THE INVENTION The present invention provides a method for producing a membrane for a fuel cell having an electrode catalyst layer on an ion exchange membrane, which is easy to produce and can be mass-produced with stable quality. Is.

[0012]

Means for Solving the Problems The present inventors have manufactured a membrane for a fuel cell having an electrode catalyst layer in advance in order to produce a bonded body of an ion exchange membrane and an electrode which is easy to manufacture in a large amount and has stable quality. As a result of various studies by the method described above, the present invention has been completed. In the present invention, a mixed solution of carbon particles carrying fine particles of an electrode catalyst and a fluorinated sulfonic acid polymer is applied on a fluoropolymer sheet having a sulfonic acid precursor, dried at 100 ° C. or lower, and then 1
A method for producing a membrane for a fuel cell having an electrode catalyst layer on the surface, which comprises heat-treating in a temperature range of 20 ° C to 250 ° C, and further introducing a sulfonic acid group into the fluoropolymer sheet having the sulfonic acid precursor.

A fuel cell is an electrochemical device that directly converts chemical energy into electrical energy by oxidizing a fuel supplied to the cell, and although there are several types depending on its structure, the present invention can be used. A fuel cell using a solid polymer electrolyte as an electrolyte, particularly a fluorine-based proton exchange polymer film. Hereinafter, in the present invention,
The fluorine-based proton exchange polymer film is called an ion exchange membrane.

In a fuel cell to which the present invention is applied, electrodes are bonded to both sides of an ion exchange membrane in general, and fuel (for example, hydrogen) is supplied to one of the gas diffusion electrodes and the other is supplied to the other. Has a structure in which an electrode reaction occurs when an oxidant (for example, oxygen or air) is supplied. In the fuel cell, the fuel supplied by the electrocatalyst is oxidized to generate protons, that is, hydrogen ions, and reaches the other electrode by ion conduction in the ion exchange membrane to cause a reaction to generate water by the oxidant. There is.

The ion exchange membrane is intimately bonded to the electrode of the fuel cell, and is used by being substantially formed integrally with the electrode. Therefore, the ion exchange membrane must have both a role as an electrolyte for conducting hydrogen ions in the fuel cell and a role as a diaphragm for preventing the fuel and the oxidant from directly mixing even under pressure.

The ion exchange membrane used in such a fuel cell is a proton exchange type polymer film having a plurality of acid functional groups chemically bonded to the polymer main chain, and may be, for example, sulfonated polystyrene. It may be a substantially fluorinated sulfonic acid polymer. However, in terms of durability, fluorinated sulfonic acid polymers are often used.

In the present invention, first, an electrode catalyst particle is added to a solution containing a sulfonic acid type ion exchange resin component in a film-like material containing a sulfonic acid precursor before introduction of a sulfonic acid group as an ion exchange membrane. A dispersion of the carbon particle powder supporting is directly applied and dried at a temperature of 100 ° C. or lower to form an electrode catalyst coating layer.
Heat treatment is performed in the temperature range of ℃ to 250 ℃. By doing so, the layer containing the carbon particles supporting the electrode catalyst becomes homogeneous and strong, and does not peel or fall off.

The formed film having the electrode catalyst layer is further hydrolyzed with, for example, a mixed solution of dimethylsulfoxide and caustic potash, and further immersed in a sulfuric acid solution to form an acid type ion exchange membrane and an electrode catalyst layer. It was very convenient because it was not affected by the treatment of the joined body. But,
If the temperature for drying after applying the solution containing the ion exchange resin component is 10 ° C. or less, it takes time to dry, which is not preferable. Also, drying at a temperature of 100 ° C. or higher is not preferable because the drying speed is too fast and bubbles are generated in the coated electrode catalyst layer, or peeling is partially generated. Therefore, the drying temperature is preferably 20 ° C to 100 ° C, and more preferably 40 ° C to 80 ° C.

If the ion-exchange resin component is applied and then dried sufficiently, it does not matter even if the temperature is raised to 100 ° C. or higher. Rather, heat treatment in a temperature range of 120 ° C. to 250 ° C. is even more effective in order to improve the strength of the coated electrode catalyst layer. At a temperature lower than 120 ° C., a coating layer having sufficient strength cannot be obtained, and the coating layer may be peeled off by a subsequent treatment, which is not preferable. Further, heat treatment at a temperature higher than 250 ° C. is not preferable because the coating film is deteriorated.

It is not clear for what reason a bonded body of an electrode and an ion exchange membrane having excellent adhesion can be obtained by such a method, but if the ion exchange resin component of the coated electrode catalyst layer remains in a dry state. There is a possibility that the ion-exchange resin component will have a stable structure at the molecular level when heat-treated at 120 ° C or higher, rather than a dense structure, and that there is almost no water because no ion-exchange group is introduced into the membrane sheet. It may also be the cause.

When an ion exchange membrane having an electrode catalyst layer is industrially produced by such a production method, a roll of a sheet containing a sulfonic acid precursor is applied to an ion exchange resin component and an electrode catalyst supporting carbon by, for example, a spray method. It is very efficient and convenient because a joined body can be continuously formed by adopting a method of applying a mixed solution of particles and then drying at 40 ° C to 60 ° C.

The film sheet containing the sulfonic acid precursor used in the present invention is preferably a fluorine-based polymer, which has the following chemical formula as a repeating unit, from the viewpoint of chemical stability.

[0023]

[Chemical 1]

The equivalent weight of the ion exchange membrane obtained by introducing an ion exchange group into the fluoropolymer is not particularly limited, but 1100 g / eq to 700 g / eq is preferable from the viewpoint of electrical conductivity. If the equivalent weight is 700 g / eq or less, there is a problem in strength and film-forming property when forming the polymer sheet, which is not preferable. Further, the solution containing the ion exchange resin component used in the present invention is preferably a component similar to the ion exchange membrane used for bonding,
For example, a polymer having the following chemical formula as a repeating unit is preferable.

[0025]

[Chemical 2]

As the equivalent weight of the ion exchange resin component,
Also from the viewpoint of electrical conductivity, 1100 g / eq or less is preferable. The carbon particles supporting the electrode catalyst to be added to the solution containing the ion exchange resin component are not particularly limited, but for example, carbon supporting platinum fine particles manufactured by E-TEK may be used, or another catalyst metal may be supported. May be However, if the carbon particles are too large, the coating formed on the ion-exchange membrane will have large irregularities, and they will come into close contact when attaching a hydrophobizing layer or a power-supplying body for taking out current when forming a fuel cell. In some cases, inconvenience may occur due to inability to obtain proper contact. Therefore, the size of the carbon particles is preferably 50 μm or less, more preferably 10 μm or less. However, if the carbon particles are too small, the inside of the electrode catalyst layer may become too thin and hinder the gas flow, so 0.1 μm or more is necessary, and more preferably 0.5 μm or more.
The hydrophobized layer here is disposed for the purpose of preventing the electrode and the power supply body from getting wet with the water generated by the electrode reaction. It is hard to get wet with water and has high electric conductivity, and the electrode is substantially It refers to the one used as an electrode that is integrated with the catalyst layer. However, this hydrophobic layer may not be necessary depending on the operating conditions.

What is taken into consideration as the composition of the coating liquid for forming the electrode catalyst layer is the mixing ratio of the ion exchange resin component and the electrode catalyst contained in the solution. If the ratio of the ion exchange resin component is too high, the distance between the electrode catalysts will increase, and in some cases, the electrical conductors, carbon, may not be kept in contact with each other and electricity may not flow, and gas diffusion may occur. The amount is also small, which is not preferable. It is preferable that the ion-exchange resin component is mixed in an amount of 0.1 to 1.0 times the weight of the carbon particles carrying the electrode catalyst fine particles. However, this mixing ratio also changes depending on the amount of the electrode catalyst supported on the carbon, and is not particularly limited to this range.

In the present invention, the solvent of the solution containing the ion exchange resin component to be applied to the membrane sheet is not particularly limited, but for example, a mixed solvent obtained by adding water to isopropanol, propanol, ethanol, methanol or the like can be used. . The thickness of the electrode catalyst layer formed on the ion exchange membrane needs to satisfy the conditions such that the amount of gas diffused into the electrode catalyst is sufficient, the amount of expensive electrode catalyst is reduced as much as possible, and the utilization efficiency is high. Therefore, if the electrode catalyst layer is too thick, a large amount of the electrode catalyst is used, resulting in high catalyst cost and insufficient gas diffusion. Therefore, the thickness of the electrode catalyst layer is 200 μm or less, preferably 100 μm or less. However, even if it is too thin, sufficient performance cannot be obtained, so 10 μm or more is necessary.

The structure of the fuel cell membrane having the above electrode catalyst layer is shown schematically in FIG. In FIG. 3, the electrode catalyst layer 27 is coated on both sides of the ion exchange membrane 26 by the method of the present invention.
The electrode catalyst layer 27 contains carbon particles 28 carrying electrode catalyst fine particles 29, and the carbon particles are partially in contact with each other to ensure mutual electric conductivity. The carbon particles 28 are covered with the ion exchange resin component 30 almost uniformly, and therefore the electrode catalyst fine particles 2
9 is also covered with the ion exchange resin component 30.
Furthermore, there are appropriate holes 31 between the carbon particles. The holes 31 have a role as gas flow holes to the electrode catalyst layer.

The composition of the coating solution must be such that the pores 31 are not completely filled with the ion exchange resin component 30 after the formation of the electrode catalyst layer or the carbon particles are not in contact with each other. The reason is that by blocking the gas flow holes, the amount of diffusion of gas into the electrode catalyst is reduced and the resistance of the electrode catalyst layer is increased, so that sufficient performance as a fuel cell cannot be obtained. Is.

When forming a fuel cell using the membrane for a fuel cell having the electrode catalyst layer thus obtained, for example, carbon and tetrafluoroethylene polymer powder are mixed on both sides of the membrane and thermoformed. The hydrophobized layer
Bonded together by hot pressing. Further, a power supply body for extracting electricity is closely attached to both sides of the power supply body and is mounted between the flanges having the gas intake port and the gas extraction port to form the fuel cell main body.

In this way, when a fuel cell is constructed using the joined body of the electrode catalyst layer and the ion exchange membrane of the present invention and electricity is taken out from oxygen gas and hydrogen gas as raw materials, ion exchange with the conventional electrode is carried out. Compared with the case of using the membrane assembly, the amount of catalyst can be reduced and the electric output can be stable for a long period of time. Thus, according to the present invention, a mixed solution of carbon particles carrying fine particles of an electrode catalyst and a fluorinated sulfonic acid polymer is applied onto a polymer sheet having a fluorinated sulfonic acid precursor, dried, and then heat treated at 120 ° C. or higher. Further, since a joined body of the membrane for fuel cell and the electrode catalyst layer is formed by the method of introducing a sulfonic acid group into the fluoropolymer sheet having the sulfonic acid precursor, it is easy to carry out industrially and a layer containing the electrode catalyst. Is a useful method for producing a bonded body which is less likely to peel off.

Next, the present invention will be described with reference to examples, but the present invention is not limited thereto.

[0034]

【Example】

[0035]

Example 1 Equivalent weight 1000 g represented by the following chemical formula
A film A containing a perfluorosulfonic acid precursor having a thickness of 100 μm and a thickness of 100 cm ² was prepared.

[0036]

[Chemical 3]

As the solution containing the ion-exchange resin component, a Nafion solution manufactured by DuPont was prepared, and as the carbon particles carrying the electrode catalyst, those carrying 20% of 25 Å platinum particles manufactured by E-TEK were prepared. . 13 parts of carbon particles carrying an electrode catalyst were mixed with 87 parts of a solution containing 5% by weight of an ion exchange resin component and stirred well,
Solution B was prepared.

Solution B was applied to one side of the film A with a brush at room temperature for 1.5 times.
g, and dried at 60 ° C. for 30 minutes with a hot air drier, then 1.5 g was similarly applied to the other surface of the film A and similarly dried at a temperature of 60 ° C. The coating coating of the film C produced as described above was strong and free from peeling, bubbles, and cracks. Next, this membrane C was heat treated in a hot air dryer at 120 ° C. for 10 minutes and then taken out to introduce a sulfonic acid type ion-exchange group, and in a solution containing 5% dimethylsulfoxide and 30% KOH at 95 ° C., 2 It was immersed for a period of time and then washed with running water for 2 hours in pure water. After that,
The fuel cell membrane D shown in FIG. 3 having a sulfonic acid type ion-exchange group after being immersed in an 8% sulfuric acid solution at 100 ° C. for 2 hours.
Got

No peeling or cracking occurred in the electrode catalyst layer during the above sulfonic acid group introduction treatment. On both sides of the obtained fuel cell membrane D, 80 parts of carbon black and 20 parts of fine powder of polytetrafluoroethylene were mixed and thermoformed at 350 ° C. in a nitrogen atmosphere to form a hydrophobic layer 2
The pieces were joined together by hot pressing at 00 ° C. Further, a power supply body for extracting electricity was closely attached to both sides of the power supply body, and the power supply body was installed between the flanges having the gas inlet and outlet to form a fuel cell body.

In this way, a fuel cell is constructed using the bonded body of the electrode of the present invention and the ion exchange membrane at 55 ° C.
Oxygen gas and hydrogen gas were supplied under the conditions of atm, and the battery performance was measured. The result is shown in FIG. It can be seen that the fuel cell characteristics are sufficiently high when the membrane for fuel cell manufactured by the manufacturing method of the present invention is used.

[0041]

Example 2 A film exactly the same as the film A of Example 1 and having a width of 1.0
A membrane E having a length of m and a length of 50 m was prepared, and a solution F which was exactly the same as the solution B of Example 1 was also prepared. The solution F was put in the solution tank 1 of FIG. 1, the membrane E was set on the feed roll 2, and the electrode catalyst layer was continuously formed on the membrane E while being wound from the winding roll 3 at a constant speed. The film E sent out from the roll 2 has a solution F of 15 m on one side in the spray chamber 4.
Spray application is performed so that the amount of g / cm ² is applied, and then the hot air dryer 5 in which hot air of 60 ° C. is flowing is passed therethrough for 30 minutes and wound by the winding roll 3. It was Further, to apply the back side, it is set again on the feed roll 2 and fed into the spray chamber 4 to obtain a solution F of 15 mg /
cm ^{2 is} applied and enters the hot air dryer 5 where it is the same as before 3
It was allowed to pass over 0 minutes and wound again on the winding roll 3. The film E coated on both sides and dried was set on the feed roll 12 in FIG. In the heat treatment chamber 13, 1
After being treated at a temperature of 50 ° C. for 10 minutes, it was introduced into a saponification tank 14 for introducing ion exchange groups. The saponification tank 14 was filled with a solution containing 5% of dimethylsulfoxide and 30% of potassium hydroxide and kept at 95 ° C. After passing through the saponification tank 14 for 2 hours, it was washed with pure water in a water washing tank 15 and wound into a tubular shape with a polyethylene spacer by a winding roll 16.

The film E taken up by the take-up roll 16 was immersed in the equilibrium tank in a tubular shape. Equilibrium tank is 100 ℃ 8
% Sulfuric acid is filled therein, and after immersion here for 8 hours, it is washed in a tank filled with pure water in a tubular shape, and finally an electrode layer similar to the fuel cell membrane D of Example 1 is formed. A large-sized membrane G for fuel cell having was obtained. During the treatment during this time, no cracks or peeling were observed on the surface of the bonded body, and a large size of the bonded body could be manufactured.

[0043]

Industrial Applicability According to the production method of the present invention, a membrane for a fuel cell having an electrode catalyst layer can be industrially easily implemented and can be mass-produced with stable quality.

[Brief description of drawings]

FIG. 1 is an explanatory diagram of a manufacturing process according to a second embodiment of the present invention.

FIG. 2 is an explanatory diagram of a manufacturing process according to a second embodiment of the present invention.

FIG. 3 is a cross-sectional view schematically showing a fuel cell membrane having electrodes on the surface of the present invention, and a partially enlarged view thereof.

FIG. 4 is a graph showing a characteristic of an output current and an output voltage of a fuel cell, which is formed by using the membrane for a fuel cell of the present invention.

[Explanation of symbols]

1 Solution Tank 2 Feed Roll 3 Winding Roll 4 Spray Chamber 5 Warm Air Dryer 6 Coating Liquid for Forming Electrode Catalyst Layer 7 Spray Gun 8 Warm Air Inlet 9 Warm Air Outlet 10 Coating Liquid Feeding Pump 11 Support Roll 12 Feeding Roll 13 Heat Treatment Chamber 14 Saponification Tank 15 Water Washing Tank 16 Winding Roll 17 Hot Air Outlet 18 Hot Air Inlet 19 Inverting Roll 20 Saponification Liquid 21 Pure Water 22 Polyethylene Spacer 23 Membrane after Coating and Drying Electrode Catalyst Layer 24 Membrane with exchange group introduced 25 Support roll 26 Ion exchange membrane 27 Electrode catalyst layer 28 Carbon particles 29 Electrode catalyst fine particles 30 Ion exchange resin component 31 Porosity 32 Polyethylene spacer roll 33 Partition plate

Claims (1)

[Claims] 1. A mixed solution of carbon particles carrying fine particles of an electrode catalyst and a fluorinated sulfonic acid polymer is applied on a fluoropolymer sheet having a sulfonic acid precursor and dried at 100 ° C. or lower, and then 120 A method for producing a membrane for a fuel cell having an electrode catalyst layer on the surface, which comprises heat-treating in the temperature range of ℃ to 250 ℃, and further introducing a sulfonic acid group into the sheet having the sulfonic acid precursor.